The present invention relates to an optical lighting system for efficiently collecting and directing light, for example, downwardly from a ceiling fixture.
Halogen directional light sources (e.g., MR16 and MR11 lamps) have been used for localized lighting applications, such as task-, accent- and down-lighting. However, since these halogen sources use filaments, they characteristically have low light-delivery efficiency. For example, an EXT lamp, a 50-watt narrow-beam halogen source, typically delivers about 500 task lumens with an energy expenditure of about 55 watts (with an electronic converter) or 60 watts (with a transformer) for a delivered efficiency of about 8-9 lumens per watt. This is for the simplest optical system. In applications where considerable beam conditioning is required through the use of multiple lenses, for example, efficiencies can drop to 5 lumens per watt or less. In addition, because the filament evaporates over time, practical lifetimes are typically limited to 4000 hours or less. Further, thermal considerations limit the practical operating power limits of these sources to about 75 watts, and, therefore, the light output to about 700 lumens or less, for the applications discussed above. Often, larger light outputs would be desirable for each light pointxe2x80x94e.g., for down-lighting applications.
In recent years, owing to the desirability of replacing the foregoing directional filament-type sources with more efficient gas discharge-based alternatives, a number of new directional lamps types have been developed. Unfortunately, owing to the added optical, size and color-averaging requirements of the discharge sources used, the use of conventional imaging optics has resulted in directional light sources that, while significantly more efficient and with lifetimes significantly longer, are also significantly larger than the directional halogen sources they seek to replace. The smallest directional discharge sources are packaged as PAR30 lamps, about 2 times the size of an MR16 lamp and 3 times the size of an MR11 lamp. It would, therefore, be desirable to provide a discharge-based directional light source that could be of the size of a directional halogen source (MR16 or MR 11) while preserving the discharge efficiency, light-output capacity and lifetime of discharge-based sources. It would also be desirable to be able to split the light output simply and with comparable efficiency where a second directional output is required. (For larger numbers of outputs, e.g. six, fiberoptic approaches may be preferable.)
An exemplary embodiment of the invention provides an efficient system for directing light, comprising a light source and a generally tubular, hollow coupling device. The coupling device has an interior light-reflective surface for receiving light from the source at an inlet and transmitting it as a generally diverging light beam through an outlet. The device is shaped in accordance with non-imaging optics and increases in cross sectional area from inlet to outlet so as to reduce the angle of light reflected from the surface as it passes through the device.
The foregoing system provides a discharge-based directional light source that can be of the size of a directional halogen source (e.g., an MR16 or MR 11 lamp) while substantially preserving the discharge efficiency, light-output capacity and lifetime of discharge-based sources. This results from the coupling device that provides light with good spatial uniformity in light intensity and color.
Embodiments of the invention can simply split the light to multiple (e.g., two) destinations with substantially the same efficiency.